[ntp:questions] FreeBSD with Garmin GPS 18 LVC

Michael L. Semon mlsemon33 at verizon.net
Sun Mar 4 21:32:49 UTC 2007


Keith E. Brandt, M.D. wrote:
> I'm trying to set up a server on a FreeBSD 6.2 system with the Garmin 
> GPS 18 LVC as the PPS source.
> 
> The system works fine using pool servers (PPS not enabled), but as 
> soon as I try to use the PPS signal, it acts as if ntpd is not 
> running (I get a "localhost: timed out, nothing received" error on 
> ntpq queries).
> 
> I'm seeing good data from the GPS using minicom to look at the data 
> stream and I have 4 - 6 satellites locked.
> 
> My ntp.conf file contains:
> 
> driftfile /etc/ntp.drift
> server 0.us.pool.ntp.org   iburst
> server 1.us.pool.ntp.org   iburst
> server 2.us.pool.ntp.org   iburst
> #
> server 127.127.20.1  mode 1   prefer
> fudge 127.127.20.1 time1 0.000   flag3 1 refid PPS
> 
> (when I comment out the last two lines, it works - obviously without 
> the PPS ref)
> 
> Suggestions?
> 
> Keith

Read David's page and take Harlan's advice from this thread.  If you are 
running a stock kernel and haven't set PPS_SYNC as outlined in David's 
page, leave the "flag3 1" out of the fudge line.  The stock kernel 
doesn't support hardpps, but the kernel does support PPSAPI so that ntpd 
can still use the PPS.

Maybe the PPS output is turned off.  Neither ntpd nor FreeBSD seem all 
that happy when it's configured for a PPS and one is not present.  The 
relevant sentences are these:

"$PGRMCE*0E<CR><LF>" to make the GPS output the current PPS and other 
settings.  Field 12 is PPS output and Field 13 is PPS pulse length.

"$PGRMC,,,,,,,,,,,,2*79<CR><LF>" to activate the PPS output, and

"$PGRMI,,,,,,,R*3F<CR><LF>" to do a soft reset of the GPS.

Other than that, check your serial ports, GPS settings, and symbolic 
links.  For "server 127.127.20.1", the NMEA driver expects /dev/gps1 to 
point to your serial port, and both the serial port and the GPS should 
be set to 4800 baud.  All of this can be changed later--with maybe one 
tweak to ntpd/refclock_nmea.c of the ntpd source code--but first try to 
get it running at 4800 baud.

Michael




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